Computed tomography (CT) imaging systems are a commonly used medical imaging tool. CT imaging, also sometimes referred to as computerized axial tomography (CAT) scanning, is based on the variable absorption of X-Rays by different tissues. CT imaging systems generate cross-sectional images of a subject.
A typical CT imaging system includes an X-Ray tube and a series of X-Ray detectors, mounted opposite the X-Ray tube, on a circular gantry. During imaging, a patient is placed on a table that passes through the center of the gantry. As the patient passes through the gantry, the gantry rotates around the patient. The X-Ray tube and X-Ray detectors on the gantry capture images of the patient from many different angles. A computer then compiles these images and produces a three-dimensional representation of the patient.
If the table moves continuously through the gantry as the gantry rotates around the patient, as occurs in many conventional CT imaging systems, the images are produced in a helical pattern. This procedure is commonly referred to as helical scanning.
The X-Ray tube in CT imaging systems typically comprises an electron beam source (cathode), a backscattered electron beam collector and an electron beam target (anode). The electron beam source, collector and target all function in generating the X-Ray beam that is used for imaging. The X-Ray beam in CT imaging systems is typically produced having a fan-shaped pattern. The shape of the X-Ray beam can be altered using a collimator, e.g., to increase or decrease the width of the beam.
The generation of the X-Ray beam by the X-Ray tube creates enormous amounts of heat, especially in the areas surrounding the electron beam target. Ninety-nine percent of the primary electron beam power is converted to thermal energy in the tube, while one percent is converted to X-Ray energy. This heat has to be removed to maintain proper operation of the X-Ray tube. Current CT imaging system designs employ forced convection cooling of the X-Ray tube using a working fluid which is then pumped to a remote fluid-to-air heat exchanger. The remote fluid-to-air heat exchanger cools the working fluid by forced air cooling. This low power density solution is mass and geometry inefficient.
Further, during imaging, it is important that patients stay very still, to prevent blurring of the image by motion. In some instances, e.g., during chest scans, in order to prevent motion, patients must hold their breath. This can be difficult and uncomfortable.
Thus, to minimize this trauma, designers are seeking to increase gantry speeds, so as to decrease the scanning time. This requires higher power levels at the X-Ray tube. Higher power levels mean higher levels of heat generation. These higher heat levels, however, can reach, or exceed, the capacity of current cooling systems. Therefore, more effective and efficient cooling techniques for CT imaging systems are needed.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for improved CT imaging cooling systems.